1. Field of the Invention
The present invention relates to a three dimensional graphics processing apparatus capable of efficiently using a limited number of computing units and performing a highly consistent polygon edge drawing process and an anti-aliasing process at a higher speed without degrading the precision of the calculation, which can be used in a display unit for a gaming device capable of displaying computer graphics (CG). The present invention also relates to an image display apparatus including the three dimensional graphics processing apparatus, a three dimensional graphics processing method using the three dimensional graphics processing apparatus, a control program for making a computer execute the steps of the three dimensional graphics processing method, and a computer-readable recording medium on which the control program is recorded, for example.
2. Description of the Related Art
Conventionally, a filtering method is known as an anti-aliasing method (i.e. a method for processing jagged edges so that they are less noticeable) used in drawing a three dimensional graphic in the computer graphics (CG). This filtering method includes blending the color data of each drawing point with the color data of surrounding drawing points based on the weighted coefficients for each drawing point in the generated image data, and displaying result of this blending on a display screen.
This filtering method requires a small amount of calculation, although the quality is relatively low. This filtering method is also capable of independently obtaining blending results of drawing points on the respective scanning lines. As a result, the circuit configuration can be simplified compared to another drawing method which requires a frame buffer, thereby reducing the required resources.
A method for changing color of the drawing point based on the displacement from the polygon edge to the drawing point is known as the art. According to this method, the displacement from the polygon edge to each drawing point is calculated in order to draw the polygon edge, the color of the drawing point determined as being in a vicinity of the polygon edge is changed based on the displacement. Thus, it is possible to draw an anti-aliased polygon edge.
This method is disclosed, for example, in Japanese laid-open publication No. 6-4679 which is titled “Image processing apparatus”. The apparatus disclosed in this reference includes a calculating means for sequentially calculating a linear expression in a two dimensional coordinate system for each edge of the polygon (i.e. each polygon edge), for determining a relative positional relationship of the drawing point with respect to the polygon, and for obtaining the displacement of each drawing point from the edges of the polygon. The apparatus disclosed in this reference further includes a changing means for changing the color or a tone of the color of the drawing point in the vicinity of the edges of the polygon based on the displacements obtained in the calculating means. The internal region of the polygon is either painted out or is shaded on the bit map memory.
However, in the conventional anti-aliasing method described above, the polygon edge must be expressed by a linear equation f(x, y)=ax+by +c, and this linear equation f(x, y) is must be calculated using an area DDA (Digital Differential Analyzer; linear interpolation circuit), in order to obtain the displacement from the polygon edge to each drawing point. The color value of each drawing point is determined by referring to a table based on the displacement from the polygon edge to each drawing point and the inclination of the polygon edge, and then the color value is written into a frame buffer having a size corresponding to the actual display screen for storing display image data.
However, since this method requires using an area DDA, a frame buffer capable of storing at least one frame is required for storing display image data. This causes a problem that more memory space is required as the number of dots increases. This also causes another problem that a fixed amount of calculation occurs constantly regardless of the characteristics of the polygon edge, and therefore the calculation time becomes longer. This is because the same calculation method is applied regardless of the characteristics of the polygon edge (e.g. a left edge or a right edge, a positive value or a negative value of the increment in the X-axis direction, the inclination of the polygon edge).
The present invention is provided to solve the conventional problems described above. The object of the present invention is to provide a three dimensional graphics processing apparatus capable of performing an anti-aliasing processing in an sufficient manner, without using the conventional area DDA and any frame buffer required for the area DDA, by using a line buffer as an area for storing display image data to reduce the required memory area, while the increase of the calculation time is restricted by performing calculation suitable for the polygon edge without degrading the precision of the calculation, an image display apparatus including the three dimensional graphics processing apparatus, a three dimensional graphics processing method using the three dimensional graphics processing apparatus, a control program for making a computer execute the steps of the three dimensional graphics processing method, and a computer-readable recording medium on which the control program is recorded.